I know it's been a topic for discussion a number of times, how exactly a Vampire would be able to acheive an erection for penetrative intercourse if they have no circulation. Here's a possible way around that/explanation.

*this of course presumes that the Vampire is essentially a corpse that moves*

Mod edit: the article linked was reproduced in full. The text has been removed but the link left in place. If you want to read about post-mortem erections in humans, then by all means, follow the link.

"Vampires are outside the realms of human constructed notions of sexuality"

I will go down with this ship And I won't put my hands up and surrender There will be no white flag above my door I'm in love and always will be

I figured that they are supernatural anyway, according to canon, and don't need to follow regular rules of human anatomy. Look at the examples of sweating, tears, working out to build up muscles...why would a vampire have those human attributes? How do they drink alcohol if they have no digestive system, but that was evident in the show too? Moonlight made up their own rules of vampirism, and they don't have to have any relation to real life.